Abstract: An optical radar system includes a laser diode and an external cavity formed by a partial reflector for reflecting a first portion of the laser beam back into the diode. A second portion of the beam is passed out of the external cavity for backscatter thereof from a target back into the diode. The emission thereby has a beat frequency related to the velocity of the target. A frequency chirp is introduced by mechanically oscillating the partial reflector longitudinally resulting in a modulation frequency in the emission corresponding to the range of the target. A photodetector and processor are used to determine the velocity and range.

Abstract: The invention performs coordinate measurement employing multiple-frequency intensity-modulated laser radar. A laser diode source is intensity modulated by variation of its excitation current. Its output beam is directed to a target using scanning mirrors or other opto-mechanical means, and the light returned from the target is detected. The modulation frequency is alternated between two or more values, creating a dataset of several relative phase measurements that uniquely determine the distance to the target without ambiguity.

Abstract: An optical frequency mixing apparatus is provided. Mixing of a frequency of an incident light intensity and a frequency (f.sub.3) of an AC signal generated by a signal generator, i.e., product calculation of the two signals is executed by a photoconductive photodetector of a photodetecting unit. This apparatus has a large allowance for unnecessary incident light such as background light and output characteristics having satisfactory linearity with respect to the incident light intensity, and can deeply set gain modulation. One of the frequency components of the sum and difference between the two signals, which is obtained as a result of product calculation, is selected and extracted using a frequency selector. As an incident optical signal, one optical signal whose light intensity has an AC component (frequency=f.sub.1) may be used. Alternatively, two optical signals whose light intensities have different frequencies (frequencies=f.sub.1 and f.sub.

Abstract: An amplitude modulated continuous wave (AMCW) laser radar (ladar) system is provided with a dual-wavelength source 10 which provides a dual wavelength signal 12 (one fixed and one chirped) which is launched down a fiber 28 to a target 38 and reflected back along the fiber 28 and the return detected by a detector 52. The transmitted signal is detected by a detector 56. The detectors 52, 56 provide an electrical return beat signal and reference beat signal, respectively, indicative of the difference between the wavelengths incident thereon. The signals are fed to a frequency mixer 60 which subtracts the two beat frequencies and signal processing logic 64 computes the distance to the target 38. Using dual wavelengths and beat frequencies provides a much broader chirp bandwidth than conventional ladar techniques, and allows for higher power sources, thereby reducing range error.

Abstract: Laser light from LD (laser diode) is guided through a fiber to be projected onto a reflector. A receiver detects a return beam of modulated light reflected by the object and outputs a signal reflecting a phase difference between the laser light and the modulation signal. The frequency of the modulation signal is changed based on the signal value so as to finally achieve phase lock. When the phase lock fixes the frequency of the modulation signal, the frequency always corresponds to a distance from LD to the reflector or a group index of a substance filling the optical path. Thus, the distance to the object or the group index of the substance filling the optical path at the time of phase lock can be determined in a simple manner and with a high accuracy, based on the output frequency at the time of phase lock.

Abstract: In a laser radar system, in which pulses from a laser are focused by a telescope onto a target, the back-scattered radiation being deflected by polarizing beam splitter onto a detector in conjunction with a reference beam, the reference beam being produced from pulses derived from the pulse laser by the beam splitter, the pulses making repeated journeys around a cavity and a proportion of the pulse being emitted each time so that each input pulse produces a multiplicity of output pulses to form the reference beam, thereby avoiding the need for a separate laser for the reference beam.

Abstract: A laser Doppler velocimeter. A laser produces a single frequency beam which is split into a probe beam and a reference beam. The probe beam is directed at a moving target and a portion of the light reflected from the target is collected, formed into a beam. Both the reference beam and the reflected beam passed through an atomic line filter in which a vapor cell is subjected to a constant magnetic field and a second magnetic field which is being oscillated. Light of the reference beam and the reflected beam passing through the filter is detected and analyzed at the frequency of oscillation of the second magnetic field and at twice that frequency. The speed of the target can be determined from measurements with respect to each beam of the amplitudes at these two frequencies.

Abstract: The heterodyne detection efficiency of coherent laser radars is maximized coaxially aligning the local oscillator (LO) beam and the received laser beam when combined at the detector by preventing interference between the counterpropagating waves in the lasing rod within the lasing cavity by using optic polarization, magneto-optic polarization, and cavity end partial reflectors.

Abstract: Laser active imaging system allowing in particular to use a wide field by means of a detecting device including a linear array of N juxtaposed photodetector elements oriented along the direction of scanning and associated with a focusing lens. The receiver includes a circuitry receiving the N detected channels and is equipped with compensation circuits for the time shift exhibited by the video signals as a function of the distance so as to bring the illuminated objects back to their angular location for the display of the observed field. The processing circuits include circuits for measuring the amplitude and the Doppler shift and for identification of the distance through the rank of the detection channel.

Abstract: A system is provided that corrects the undesirable fast power modulation observed at an output of a wideband frequency modulated (FM) laser. The correction is accomplished by applying a corrective voltage to an amplitude modulated (AM) modulator. The response of the laser is first measured to characterize the laser. Iterative predictions of appropriate voltage correction waveform, based upon the observed power modulation and the laser's response are then applied to the AM modulator to reduce the unwanted laser power modulation.